The present invention relates to coin evaluators and in particular, to a capacitance sensor for coin evaluation. There are a number of different sensors designed to evaluate metallic coins. Inductive sensors are commonly used and are sensitive to many inherent characteristics of coins simultaneously. Inductive sensors are responsive to magnetic permeability of the coin material, conductivity, quantity of the material and size of the coin. The simplest inductive sensors produce a response that depends on all of these characteristics, and as such, the resulting security is not high. Some inductive sensors attempt to measure the separate contributions of these characteristics, however, this requires a significant increase in the sophistication of the coin acceptor and its electronic evaluation system.
An alternate approach to improve the security of coin acceptors, is to have additional non inductive sensors. These sensors can provide a separate evaluation of the same characteristics that are influencing the inductive sensor signal (e.g., the coin diameter) or other characteristics such as coin weight. In the first case, the additional sensors can distinguish some of the characteristics influencing the inductive sensor signal while in the second case additional information is obtained.
In general, coin forgery is unprofitable primarily due to the low value of the coins. Unfortunately, coins of two countries which are of drastically different real values may be indistinguishable by coin acceptors because the coins are basically the same, other than the impressed patterns on the coins. Similarly, some industrially produced metallic washers without stamping on their surfaces are also indistinguishable from some coins by many coin acceptors.
There remains a need for an effective sensor which is most effective and is effective in distinguishing coins.